The present invention relates to a method of manufacturing a ceramic member having a plurality of fine through holes.
A member comprising a thin plate having a plurality of fine through holes and being supported by a rigid plate is used as a component of an ion current control head, high-precision electric field shutter, encoder, scale or the like to detect or record a position by controlling the emission of a gas, liquid, fine particle solid, light or the like from the fine through holes.
Materials such as a metal, synthetic resin or the like have conventionally been used for such a member. To meet the demand for higher density, precision and reliability, a ceramic member has become the main stream of the market in recent years.
In the above ceramic member, as for the support of a thin plate by a rigid plate, a thin plate 7 may be supported by different rigid plates 9 at both sides of a portion 30 having fine through holes as shown in FIGS. 1A and 1B, or may be supported from around a portion 3 having fine through holes 1 by forming window portions 3 in the rigid plate 9 and laminating the thin plate 7 upon the rigid plate 9 such that the portions 30 having fine through holes 1 cover the window portions 3 as shown in FIGS. 2A to 2C and 3A to 3C. FIGS. 4A to 4C show a ceramic member 2 prepared by laminating a rigid plate 9 consisting of 3 layers having differently shaped window portions 3 upon a thin plate 7 having fine through holes 1.
Supporting the thin plate by the rigid plate is intended to improve the rigidity of the ceramic member so as to make it more practical in manufacture and use.
A ceramic member in which a thin plate having a plurality of fine through holes is supported by a rigid plate is manufactured by making a green sheet for the thin plate and a green sheet for the rigid plate, laminating the green sheet for the thin plate upon the green sheet for the rigid plate to form an integral laminate and firing the laminate from a viewpoint of improving dimensional stability after firing. That is, since the thin plate has a plurality of fine through holes, if it is fired alone, it is readily distorted by firing shrinkage. Although the fine through holes are formed by punching before firing, they may be formed before the green sheet for the thin plate is laminated upon the green sheet for the rigid plate or after they are joined together into an integral laminate.
In recent years, it has been desired to further reduce the thickness of the thin plate from a viewpoint of improving the resistance for passing a gas, fine particle solid, liquid or the like and the uniformity of an electric field and further reduce the size of and the interval between fine through holes from a view point of increasing density. More specifically, it has been desired to reduce a thickness of the thin plate after firing to 100 .mu.m or less, preferably 50 .mu.m or less and both a minimum value of the size of fine through holes and a minimum value of the interval between adjacent fine through holes after firing to 150 .mu.m or less.
However, since the strength of a ceramic green sheet generally lowers when the thickness thereof decreases, there is such a problem that a crack or a defect causing a crack is generated between the fine through holes during the formation of the fine through holes in the green sheet for the thin plate by punching when the thickness of the thin plate is further reduced. Cracks are readily generated in the process of laminating the green sheet for the thin plate upon the green sheet for the rigid plate or by stress at the time of firing and further the above defect develops into a crack at the time of use in many cases, thereby impairing the reliability of a product. When such a crack or defect is generated, the interior wall of the fine through hole becomes rough and the resistance for passing a gas, liquid or the like increases. When an interval between adjacent fine through holes is further reduced, a crack or defect is readily generated likewise.
Meanwhile, as the green sheet generally has the property of stretching easily when it is made thin, when the thin plate is made thinner, the green sheet for the thin plate stretches when it is punched or handled, thereby deteriorating the positional accuracy of the fine through holes. As a result, there is such a problem that a defect such as a crack is readily generated between the fine holes.